The Waiwhero wetland (16 ha) is one of the largest wetlands in the Rosedale Hills, 35 km north-west of Nelson, New Zealand. It has an extensive cover of Salix fragilis L. (crack willow) and has been hypothesised to be a source of groundwater recharge for the Moutere aquifers, an important local groundwater system. However the wetland could also be a groundwater discharge zone, because of the geological boundary that it straddles. The overall aim of this study was to determine the direction of groundwater flux of the wetland by measuring the water balance, with particular emphasis on the transpiration rates from the crack willow trees. The average daily transpiration (measurement was for 230 days) of crack willows in the wetland (6.4 mm/day) was close to twice the potential evapotranspiration (PET) for grassland (3.9 mm/day). The highest measured willow transpiration rate was 12.4 mm/day and the lowest was 0.8 mm/day. High transpiration from crack willows was due to the horizontal energy fluxes (advective energy), tree physiological characters and high soil water content. The study established that the wetland is a groundwater discharge zone with, on average for the two summer periods (2008 and 2009), the net groundwater discharge being 4.8 mm/day. The daily water balance results between two major rainfall events showed that the initial discharge source was from the surrounding hills and later stabilized at around 6 to 14 mm/day. It was believed to be a contribution from the shallow and deep aquifers or a combination of local region inflow and aquifers. The water balance showed that the main loss of water through the hydrological system of the wetland during summer was from the high transpiration of willows (7.7 mm/day). The extent of water savings estimated for the 16 ha wetland through a hypothetical situation of willow removal, and the assumption that it is filled with open water without any canopy cover, was 688 m3/day. However this water savings rate if applied to a large area of crack willow stands would be quite high. On similar lines it is important to understand the transpiration rates of other wetland tree species in New Zealand. This information would help in preparing regional council plans for the introduction of tree species in the wetland for better management of the water resources and sustainable ecosystem management.

This study aims to determine the recharge, discharge and the mixing mechanisms of a complex aquifer system located above the Kazan trona ore field using the environmental isotopes of deuterium, oxygen-18, carbon-13 and carbon-14, chlorofluorocarbons (CFC- 11, CFC-12 and CFC-113) and the noble gas isotopes (He, Ne, Ar, Kr and Xe). The groundwater system consists of three different aquifers: shallow, middle and deep. The Akpinar formation lying between deep and middle systems acts as an aquitard. Oxygen-18 and deuterium data showed an isotopic contrast between the shallow and deeper aquifer systems and even between the unconfined and confined parts of the middle and deep aquifers. The Noble gas temperatures indicated the average yearly air temperatures in shallow aquifer system whereas the recharge temperatures came out to be lower than todays in deep groundwater system. This finding is also supported by the dissolved inorganic carbon&rsquo / s radiocarbon activities being close to the detection limits in the same system. These activities together with the stable isotope data revealed there might be evidence of recharge to the middle and deep aquifer systems under colder climate conditions during the late Pleistocene. CFC concentrations indicated modern recharge to the shallow aquifer system, whereas the concentrations were close to the detection limits therefore CFC&rsquo / s were unable to date the middle and deep aquifer systems however proved the existence of modern recharge to this system. Mantle-He escape to shallow aquifer system is believed to be along a deep buried fault system located in downgradient areas.